it was all just a dream. with all the dealings jake has had with crayak and elimmist its entirely likely he would dream up a voice saying something like that at the end of a dream.
Quiote possible, but if it was it's not something KA would ever admit to, as "it was all a dream" endings suck, which is why I choose to believe this isn't the case (even though it does seem like the most likely scenario).
See, I would disagree with that, if only in this one example. Most "it was all a dream" endings DO suck, yes. But in this one case, it actually /works/. You can see it coming, for one thing, because reality is not making sense (even less so than usual in Animorphs, in any case). Thus, you begin to suspect it's a dream from the start and so it doesn't feel like just an author's cop-out.
And it still is a very strong statement about Jake's character and state of mind at that point in the series, even if it is a dream (heck, perhaps especially so). His conversation with Tobias/Elfangor can be seen as an argument with himself, for example ("We can fight a war without sacrifice"/"You know better than that").
I think the whole book (including the voice that Jake heard) could have been a dream sequence and still be an intensely wonderful and meaningful book.